Long endurance small displacement maritime submersible propulsion system

ABSTRACT

A watercraft (101), such as a submersible or submarine, is provided which includes a hull; a propulsion system (121) for propelling the hull through water; and a power plant which powers the propulsion system, the power plant including a heat engine (103) and a thermal energy source. The thermal energy source includes at least one material selected from the group consisting of nuclear isomers and radioisotopes.

FIELD OF THE DISCLOSURE

The present disclosure pertains generally to Stirling cycle engines, and more particularly to submersible maritime propulsion systems incorporating the same.

BACKGROUND OF THE DISCLOSURE

Long endurance small submersible vehicles have long been needed for scientific and military operations. To date, however, the technical difficulties associated with their design have hindered their introduction. Since electric motors are typically used for propulsion in vehicles of this type, battery technology is a principle obstacle in this application.

Small submersibles employed by the military, or by universities for oceanographic research, are typically powered by electric motors which draw their electrical current from batteries. This limits the amount of “Bottom Time” a submersible can operate at depth. Additionally, the types of batteries commonly used in other fields present hazards in this application. In particular, if sea water floods a battery compartment containing lead acid batteries, chlorine and hydrogen gas may be released from the battery compartment, thus threatening the lives of a human crew. Similarly, lithium ion batteries present a risk of fire, which can lead the catastrophic failure of the pressure hull and the death of all of those on board.

Stirling Cycle engine designs have been recently employed in littoral class submarines, with a significant degree of success. Unfortunately, this design does not lend itself well to small submersibles. Air-independent submarines of the type represented in the littoral class could just as easily employ Ericson Cycle engine designs or Rankine Cycle engine designs, but these designs are also not suitable for use in small submersibles. In particular, in these engine designs, combustion takes place in a combustion chamber enclosure external to, or isolated from, the motive gas or working fluid. Thermal energy from combustion is then transferred to the motive gas or working fluid to drive the mechanisms of the engine. Typically, this thermal energy is transferred through the walls of an array of tubes making up the heater head or boiler, and may occur through both conductive and radiative thermal energy transfer.

During operation of the external combustion engine, thermal energy from combustion is transferred to the plurality of heater tubes (and subsequently to the mechanisms of the engine) at a nearly equal rate to ensure a balanced and sustained external combustion cycle. The combustion needed for a source typically requires oxygen. The oxygen can be liquefied, as in the case of the Air Independent Submarine, or drawn from the atmosphere itself, as with the Stirling Automotive Engine developed by NASA. These systems also rely on propellers to provide propulsion. Propellers may lead to cavitation when operated at high speeds of rotation, which can generate an acoustic signature detectable by passive sonar systems.

Information disclosed in this Background of the Invention section is only for enhanced and detailed understanding of the general background of the invention. It should not be taken as an acknowledgement, or any form of suggestion, that this information forms prior art to anything disclosed herein.

SUMMARY OF THE DISCLOSURE

In one aspect, a watercraft, which may be a submersible or a submarine, is provided. The watercraft comprises a hull; a propulsion system for propelling the hull through water; and a power plant which powers the propulsion system, the power plant including a heat engine and a thermal energy source; wherein the thermal energy source includes at least one material selected from the group consisting of nuclear isomers and radioisotopes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a particular, non-limiting embodiment of a submersible which may be equipped with a propulsion system of the type disclosed herein. A portion of the outer hull of the submersible has been removed to show the details of the propulsion system thereof.

DETAILED DESCRIPTION OF THE DISCLOSURE

It has now been found that the aforementioned problems of combustion (as a heat source) and the sound generated by cavitation may be overcome with the systems and methodologies disclosed herein. In a preferred embodiment, a propulsion system for a long endurance submersible is provided that is equipped with a heat engine (such as, for example, a Stirling Cycle engine, Ericsson Cycle engine or equivalent engine design) which utilizes nuclear isomers for the heat source. Nuclear isomers have been shown to generate thermal energy through decay sufficient to power a Stirling engine in excess of 10,000 hours operation. The heat engine, drawing thermal energy from the nuclear isomer, may turn a generator to provide all the electrical power needed for the submersible to conduct military or scientific operations.

FIG. 1 depicts a first particular, non-limiting embodiment of a small displacement submersible 101 which may be equipped with a water jet eductor propulsion system 121 of the type disclosed herein. As seen therein, the propulsion system 121 includes a heat engine 103 which is preferably a Stirling Cycle engine, a generator or alternator 105, an electrically driven Tesla bladeless turbine 107, conduit piping 109, and bucket thruster system 111. The propulsion system operates to intake sea water into a first end of conduit 109 and to eject the water through a second end of the conduit 109. The conduit 109 is preferably equipped with internal vanes disposed at an approximately 37° twist from the parallel of the longitudinal axis of the conduit 109.

The outflow end of the conduit is equipped with a nozzle 113 and a quasi-conical housing 111. This housing 111 is preferably open to the sea at both ends, and acts to entrain sea water as the vortexual fluid flow exits the nozzle 109 to suppress cavitation. For reverse thrust of the system, the quasi-conical housing will maneuver to divert the flow from the nozzle 109 in a manner similar to the reverse thrust system on aviation jet aircraft engines commonly known as “bucket thrusters.” With the exception of operation in the reverse thrust mode, systems of this type may be configured to be exceptionally quiet, since there are no vibrations from reciprocating pumps or cavitation from propeller blades.

The propulsion system 121 is powered by a power plant that includes the heat engine 103 and a thermal energy source. The thermal energy source preferably comprises one or more nuclear isomer isotopes. Suitable isotopes for this purpose may include Americium (242Am), which has a half-life of 141 years and produces 49 keV; Hafnium (178m2Hf), which has a half-life of 31 years and can produce 2.4 MeV; and Molybdenum (93Mo). The use of these isotopes is advantageous in that they emit relatively small amounts of ionizing radiation. Rather, the decay energy is mostly in the thermal side of the equation, with only small amounts of beta particles emitted. To protect personnel in the submersible, the nuclear isomer pile may be coated with boron glass or obsidian glass ceramics.

The use of the foregoing types of isotopes as the fuel in a heat engine overcomes the limitations and hazards attendant to the use in submersibles of lithium or lead-acid batteries. Moreover, the endurance of the submersible may thus be based solely upon the human limitations of the operators.

Navigation and depth soundings may be augmented with blue lasers, depending on water clarity, as well as conventional systems of depth soundings and Inertial Navigation Systems. Since Stirling engines are scalable, the teachings disclosed herein may be applied to submersibles of any size, from ROVs to a submersible with more than a dozen occupants.

The above description of the present invention is illustrative and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims. 

What is claimed is:
 1. A watercraft, comprising: a hull; a propulsion system for propelling the hull through water; and a power plant which powers the propulsion system, the power plant including a heat engine and a thermal energy source; wherein the thermal energy source includes at least one material selected from the group consisting of nuclear isomers and radioisotopes; and wherein the watercraft is selected from the group consisting of submersibles and submarines.
 2. The method of claim 1, wherein the hull includes a forward end and an aft end.
 3. The method of claim 1, wherein the heat source includes ²⁴²Am.
 4. The method of claim 1, wherein the heat source includes ^(178m2)Am.
 5. The method of claim 1, wherein the heat source includes ⁹³Mo.
 6. The submersible of claim 1, wherein the submersible includes at least one generator which powers said propulsion system.
 7. The submersible of claim 6, wherein the at least one generator includes an alternator.
 8. The submersible of claim 1, wherein said propulsion system includes at least one Tesla bladeless turbine.
 9. The submersible of claim 2, wherein said turbine intakes water through a first opening in said hull and ejects water from a second opening in said hull, and wherein said first and second openings in said hull are in fluidic communication with each other by way of a conduit.
 10. The submersible of claim 9, wherein said conduit is equipped with a plurality of vanes along an interior surface thereof, and wherein said plurality of vanes are configured to induce vortexual fluid flow to the water ejected from the second opening in said hull.
 11. The submersible of claim 10, further comprising: an articulated, quasi-conical housing which terminates in a tapered end.
 12. The submersible of claim 11, wherein said tapered end of said housing extends beyond said second opening of said conduit.
 13. The submersible of claim 12, wherein the flow of water through said housing suppresses cavitation through the entrainment of ambient fluid.
 14. The submersible of claim 12, wherein said housing is maneuverable to deflect the flow of water from said second end of said conduit toward the forward end of said hull.
 15. The submersible of claim 1, wherein said heat engine is selected from the group consisting of Stirling Cycle engines and Ericsson Cycle engines.
 16. The submersible of claim 1, further comprising: at least one battery which powers said submersible.
 17. The submersible of claim 1, further comprising: at least one ultracapacitor which powers said submersible.
 18. The submersible of claim 1, further comprising a water jet eductor system.
 19. The submersible of claim 1, wherein the propulsion system includes a water jet eductor propulsion system.
 20. The submersible of claim 1, wherein the propulsion system includes a bladeless turbine. 